Vehicle wheel apparatus is adapted to freely rotatably support a wheel hub to mount the wheel via a roller bearing. An inner ring rotation type is used for a driving wheel. Both inner ring rotation and outer ring rotation types are used for a driven wheel. A double row angular ball bearing is widely used in such a bearing apparatus since it has desirable bearing rigidity, high durability against misalignment and small rotation torque that is required for fuel consumption. The double row angular contact ball bearing has a plurality of balls interposed between a stationary ring and a rotational ring. The balls contact the stationary and rotational rings and are at a predetermined contact angle.
The vehicle wheel bearing apparatus is broadly classified into a first, second, third or fourth generation structure. In the first generation, a wheel bearing of double row angular contact ball bearing type is fit between a knuckle, forming part of a suspension, and a wheel hub. In the second generation type, a body mounting flange or a wheel mounting flange is directly formed onto the outer circumferential surface of an outer member. In the third generation type, one of the inner raceway surfaces is directly formed on the outer circumferential surface of the wheel hub. In the fourth generation type, the inner raceway surfaces are directly formed on the outer circumferential surfaces of the wheel hub and the constant velocity universal joint.
In prior art wheel bearing apparatus, both bearing row arrangements in the double row bearing are the same. Thus, the apparatus has sufficient rigidity during straight away running, however, optimum rigidity cannot always be obtained during curved running. That is, the positional relationship between wheels and the bearing apparatus is usually designed so that the weight of the vehicle acts substantially in the middle between the rows of bearing balls during the straight way running. However, larger radial loads and larger axial loads are applied to the axles of the vehicle on the side opposite to the curving direction (axles of the left hand side of the vehicle when right hand curving). Accordingly, it is effective to have a larger rigidity on the outer side of the bearing row than on the inner side of the bearing row inner side in order to improve the durability and strength of the bearing apparatus. Thus, a known vehicle wheel is shown in FIG. 12. It can have high rigidity without enlargement of the bearing apparatus.
The vehicle wheel bearing apparatus is formed with a double row angular ball bearing that includes an outer member 51 integrally formed with a body mounting flange on its outer circumferential surface. The flange is to be mounted on a knuckle (not shown) of a vehicle. The outer member 51 has double row outer raceway surfaces 51a, 51b. An inner member 55 includes a wheel hub 52 with a wheel mounting flange 53 integrally formed on one end to mount a wheel (not shown). One inner raceway surface 52a is formed on the outer circumferential surface opposite to one 51a of the double row outer raceway surfaces 51a,q 51b. A cylindrical portion 52b axially extends from the inner raceway surface 52a. An inner ring 54 is fit onto the cylindrical portion 52b and is formed on the other outer circumferential surface. The inner raceway surface 54a is opposite to the other raceway surface 51b of the double row outer raceway surfaces 51a, 51b. Double row balls 56, 57 are freely rollably contained between the outer raceway surfaces 51a, 51b and inner raceway surfaces 52a, 54a of the inner member 55. Cages 58, 59 rollably hold the balls 56, 57 in place.
The inner ring 54 is axially immovably secured on the cylindrical portion by a caulked portion 52c formed by radially outwardly plastically deforming the cylindrical portion 52b of the wheel hub 52. Seals 60, 61 are mounted in annular openings formed between the outer member 51 and the inner member 55. The seals 60, 61 prevent leakage of grease contained within the bearing apparatus. Additionally, they prevent the entry from the outside of rain water or dusts into the bearing apparatus.
A pitch circle diameter D1 of the outer side ball group 56 is set larger than a pitch circle diameter D2 of the inner side ball group 57. Accordingly, the diameter of the inner raceway surface 52a of the wheel hub 52 is larger than that of the inner raceway surface 54a of the inner ring 54. Also, the outer raceway surface 51a of the outer side of the outer member 51 is larger than the outer raceway surface 51b of the inner side of the outer member 51. The number of outer side balls 56 is larger than the number of inner side balls 57. By setting the pitch circle diameter D1 of the outer side larger than the pitch circle diameter D2 of the inner side (D1>D2), it is possible to obtain a large rigidity of the bearing apparatus 50 and thus to extend its life (see Japanese Laid-open Patent Publication No. 108449/2004).
In the prior art bearing apparatus 50, a stepped portion 62 is formed on the wheel hub 52 between the inner raceway surface 52a of the outer side and the cylindrical portion 52b on which the inner ring 54 is press fit. The presence of the stepped portion 62 (height of step: (D1−D2)/2) causes a problem where the balls 56 of the outer side, temporary assembled in the outer raceway surface 51a of the outer member 51 by the cage 58, tend to contact the stepped portion 62 and a counter portion 63 of the inner raceway surface 52a of the wheel hub 52. Thus, the balls may damage the stepped portion 62 and counter portions 65 during assembly of the bearing apparatus 50.
Additionally, micro damages may be caused on the surface of balls 56, 57 during press fitting of the inner ring 54 in a state where the inner side balls 57 are temporary assembled on the inner side outer raceway surface 51b of the outer member 51. That is, the balls 56, 57 may be damaged in this temporary assembling step not only by the contact of them against the counter portion 64 of the inner ring 54 but the contact of balls with each other. The damaged surfaces of the balls 56, 57 cause noise in the bearing apparatus and reduces the life of the bearing apparatus. Accordingly, very careful assembling work is required. This reduces assembling efficiency of the bearing apparatus.